Help Needed - Enclosed Trailer Shore Power

I really want shore power in my car hauler. I bought some components I thought would work but I messed up with the sub-panel (a.k.a. load box). Plus, I'm having a hard time finding reliable resources for what components I do need and how to wire it all. The sub-panel I bought is a now discontinued SquareD and I can't make heads or tails of what internal components it needs to finish it. I'd prefer to abandon that in favor of a known group of compatible components.

I have a shore power inlet and have already installed it on the trailer. To it I attached a 4/C 6AWG cable that has red, black, green and white wires.

My goal is a 50A box (cuz bigger is better) with a couple of circuits for receptacles for now. I just need places to plug in chargers, compressor, Quick Jack, fan, a light.

Later, I'd like to add a circuit for interior lights and much later, a circuit for HVAC. I don't have any desire to power anything 12v or use solar or to mess with converters. At most, I might want to be able to power the thing off a generator but I'm hoping that would only require an adapter plug from the gen to the shore power inlet. Feel free to disabuse me of that notion.

So here's what I need:

1. Help me pick a sub-panel, breakers and whatever other internal guts for the panel I need that are all compatible with each other. Needs room for two circuits now with room for expansion for interior lights and HVAC later.
2. Explain the connections from the 4-wire shore power inlet into the panel
3. Is there anything special about shore power with respect to grounding?
4. Explain the wiring from the subpanel to, say, a receptacle. Type of wire, connections in the panel and connections on the receptacle. If it's the same as household wiring, that's all I need to know.

Hope I'm not asking too much here. I have looked at lot of different videos and references and I'm just not getting enough info, especially about the sub-panel components.

Thanks,

Jim

Study camping trailers and their wiring.

35 amp is plenty if only one A/C unit.  50 amp for two A/C.   Microwave ovens can b a huge drain.  LED lighting lessens load requirements.

#1 thing... you don't want people standing on the ground and touching the trailer becoming the ground circuit.  Can be deadly.

Purple Frog (Forum Supporter) said:

#1 thing... you don't want people standing on the ground and touching the trailer becoming the ground circuit.  Can be deadly.

So what does that mean in terms of wiring? Make sure that the trailer frame is connected to the ground in the sub-panel?

Bigger is not necessarily better. 
 

If it's a car hauler, I'm assuming it spends time at race tracks. It's likely that the pits at the tracks may not have 50A connections. The plugs are different. 
 

You don't need 50A.  That's overkill. 

Your trailer isn't actually grounded directly to ground. Tires are good insulators. Your ground is through the shore power line (green) to the connection at the venue. 
 

Yes, your frame is grounded to the sub-panel (to the shore power line). So are all of your boxes, fixtures, and devices. 
 

If you are gonna run a generator, make sure there is a disconnect so your power isn't backfeeding into the venue.

Any specific reason you want to avoid 12V? It's simple, reliable and there are millions of options for lighting available.

Your 120V circuits should be the same as a residential 120V circuit. Same breaker style, same layout. 

On that 4W, Red and Black should be hot, white common and green ground. 

Are you planning on installing an onboard genset? Or just having one to plug in to through the same connection?

SV reX said:

Your trailer isn't actually grounded directly to ground. Tires are good insulators. Your ground is through the shore power line (green) to the connection at the venue. 
 

Yes, your frame is grounded to the sub-panel (to the shore power line). So are all of your boxes, fixtures, and devices. 
 

If you are gonna run a generator, make sure there is a disconnect so your power isn't backfeeding into the venue.

Thanks. The gen would only be used if no shore power available.

I'd really consider having a couple good deep-cycle batteries (or golf cart batteries) that could provide some functions without needing shore or gen power.  You can get some really powerful 12v LED lights that would be able to light the inside and outside of your setup.  Most of your trailer convenience items are going to be 12V as well - powered awning, a winch, entertainment system, roof fans, USB charging outlets.  If you did that, I'd get a RV-style converter that would tend the batteries, provide the 12V for the accessories, and also give you the breaker box for your 120V.  You can put a solar battery tender on there to keep the batteries in good shape.

As stated, I wouldn't bother with 50A.  Pretty much everywhere you go will have 30amp and 50amp and a cheap pigtail will plug your 30amp in to those places that only have 50amp.  As long as your draw is low enough, you can adapt down from the 30amp and plug in to a regular 15 or 20 amp socket.  Just be careful with that - turning on the A/C will start to melt things.

Don't over-think your switching from the generator to shore power, either.  There are some very expensive and fancy transfer switches, but you can get there by having the generator wired only to a 30 amp receptacle.  Then when you want to use generator power, you plug your trailer in to the generator receptacle.  When you want shore power, you have to physically disconnect the generator from the trailer's input in order to switch over.  It's not a slick as an auto transfer switch or anything, but it makes it impossible to backfeed power, it won't break, and it's cheap and easy to wire up.

birdmayne said:

Any specific reason you want to avoid 12V? It's simple, reliable and there are millions of options for lighting available.

Your 120V circuits should be the same as a residential 120V circuit. Same breaker style, same layout. 

On that 4W, Red and Black should be hot, white common and green ground. 

 

Are you planning on installing an onboard genset? Or just having one to plug in to through the same connection?

Re: 12V, just trying to keep things simple. No on board genset. Just portable when needed. Hoping to just plug into the shore power inlet. But then, what serves as ground when on a generator?

wae said:

As stated, I wouldn't bother with 50A.  Pretty much everywhere you go will have 30amp and 50amp and a cheap pigtail will plug your 30amp in to those places that only have 50amp.  As long as your draw is low enough, you can adapt down from the 30amp and plug in to a regular 15 or 20 amp socket.  Just be careful with that - turning on the A/C will start to melt things.

Don't over-think your switching from the generator to shore power, either.  There are some very expensive and fancy transfer switches, but you can get there by having the generator wired only to a 30 amp receptacle.  Then when you want to use generator power, you plug your trailer in to the generator receptacle.  When you want shore power, you have to physically disconnect the generator from the trailer's input in order to switch over.  It's not a slick as an auto transfer switch or anything, but it makes it impossible to backfeed power, it won't break, and it's cheap and easy to wire up.

I already have the 50A inlet. Might as well keep it unless there's some cost I'm not understanding. Any reason I can't use an adapter to plug into a 30A receptacle? There are adapters that go both ways: https://www.etrailer.com/dept-pg-RV_Plug_Adapters.aspx

Again, trying to keep things as simple as possible. Not interested in doing a transfer switch.

Thanks for the info.

12V seems significantly easier than shore power. Many pits don't have shore, and when they do it's often at a central location. If you have 12v, you can be completely independent. You can operate with no shore power at all. 
 

The answer about grounding is... it depends. You can probably find the answer in your owner's manual. Usually, the non electrical parts of the generator are bonded to the metal frame, and the frame acts as ground (because the electrical source is the generator)

YMMV

In reply to jimgood :

You shouldn't need a transfer switch (detailed above). 
 

Technically, a 50A plug plugged into a 30A supply is backwards, and illegal. If your trailer is a 50A draw, you could overload a 30A. In your case this is extremely unlikely, because you won't be drawing 50A. But it's still not right. 
 

Its ok to plug a 30A trailer into a 50A plug, but it's not OK to plug a 50A trailer into a 30A plug. 
 

What if you sold it one day, and a future buyer saw the 50A plug and assumed he could run 50A off the trailer?

Your job when doing electrical work is to keep it safe for you, and to idiot-proof it for future users.

SV reX said:

The answer about grounding is... it depends. You can probably find the answer in your owner's manual. Usually, the non electrical parts of the generator are bonded to the metal frame, and the frame acts as ground (because the electrical source is the generator)

YMMV

I guess that makes sense.

Many times over the years I have had to plug my 50A RV into a 35A outlet.  No problem if you understand that you can't use everything onboard at the same time.   

In reply to Purple Frog (Forum Supporter) :

I agree. I've also done it many times. 
 

But your RV is actually a 50A RV. I would just wonder if a future owner might assume the trailer is 50A when it's not, and add a 2nd AC unit (or other) trying to power it through a panel and wiring that were only rated for 35A (not 50A)

SV reX said:

In reply to Purple Frog (Forum Supporter) :

I agree. I've also done it many times. 
 

But your RV is actually a 50A RV. I would just wonder if a future owner might assume the trailer is 50A when it's not, and add a 2nd AC unit (or other) trying to power it through a panel and wiring that were only rated for 35A (not 50A)

What would make the panel and wiring of the trailer rated for 50A vs 35A?

In reply to jimgood :

Just the wire sizes you use. 

I think this is what I was looking for:

In reply to jimgood :

Note that diagram has no 220V output. I don't think you need it, but if you do that's not your diagram. 

SV reX said:

12V seems significantly easier than shore power. Many pits don't have shore, and when they do it's often at a central location. If you have 12v, you can be completely independent. You can operate with no shore power at all. 

It really comes down to whether or not you want AC on the roof of the trailer.

SV reX said:

In reply to jimgood :

Note that diagram has no 220V output. I don't think you need it, but if you do that's not your diagram. 

Thanks. No, I don't need it.

I went to a couple different hardware stores and got the box figured out. This box was the SquareD that I originally purchased. I just had the wrong type of breakers (needed Homeline) and ground bus bar (needed the shorter bar, part #PK7GTA). Plus, until that diagram I posted above, I did not have a clear idea how it was supposed to be configured and wired. With the correct ground buses and breakers it starts to make sense.  If I need the extra ground bus I'll move it to the bottom left of the box. I didn't draw it but there should be a chassis ground from the trailer into the box ground.

With the 50A across the two bars and wired this way, it provides 110v to each leg. The loads are wired with common and ground separate. So this provides a 20A and 15A breaker on each leg. If I really want to be safe when only 30A is available, I could easily swap in a 30A main breaker. Or just limit the loads.